The present invention relates to a multi-dimensional image compression & decompression system, and in particular, to a multi-dimensional image compression & decompression system that performs high-efficiency image compression & decompression in a system where picture element correspondence or frame correspondence on a time axis are not guaranteed on a compression side and a decompression side and so that image transfer between apparatus of different types is possible.
Various systems have been proposed for the compression of image information. For example, when a means to divide signals levels equivalently with respect to each sample value of image signals that have been made into digital signals, and to linearly (equivalently) quantize values included in the respective ranges by replacement with a single representative value is used, it is generally necessary to change from 6 bits (64 gradations) to 8 bits (256 gradations) for natural images in cases where the difference between the representative value and the original value is not known. It is therefore necessary to handle much information with respect to each sample value if image signals are to have signals that have been digitalized by equivalent quantization as described above, are to be recorded as they are.
Coding signals using a smaller amount of information is sensitive to portions where there are few changes in the signal, and even if there is a certain degree of error in portions where there are large changes in the signals, it is possible to overcome this by the nature of human audio and visual perception being such that these are difficult to detect. Alternatively, the correlation on the time-space axis for information signals that are the object of recording can be used so that for example, after the image is disassembled into picture elements, the height of the adjacency correlation for the brightness value of each picture element is used and a small number of approximate values for the original image are transferred, the difference portion between picture elements or the difference portion between frames can be transferred, or the fact that the high-frequency component is small can be used to perform reduction of the frequency elements. These and other high-efficiency coding systems to reduce the amount of information per sample can be applied for the recording, transfer or transmission of digital data that has had the data amount compressed. In addition, another conventionally known technique involves restoring the image by performing data decompression after digital data that has had the amount of data compressed, has been received and reproduced.
In the conventional image information compression systems described above, emphasis is placed on the favorable performance of restoration of the disassembled image and so there are many cases where a condition for this is agreement between the number of picture elements between the original image and the restored image (decompressed image) and so in cases where compression and decompression operation is performed between images having different numbers of picture elements, it is necessary to separately perform interpolation and extrapolation for the picture elements after decompression has been performed. However, in conventional image information decompression methods, this does not mean that only the real, effective information is extracted and decompressed, but that the system is dependent to a certain extent upon the physical elements configuring the image.
The case where an image that has been taken by a TV camera apparatus for example, is to be used for a printing plate for an image is used here as one example where the picture element densities in two images having different numbers of picture elements are extremely different. In this case, the picture element density of an image obtained by a TV camera apparatus is high at about "500.times.500" per screen but the picture element density of an image in electronic printing is .-+.several thousands .times. several thousands" per screen and since there is such a large difference when compared to that obtained by a TV camera, an alias is generated by the picture element magnification even if a compression and decompression system is not implemented at all for the image information of the corresponding picture elements as described above, and in cases where interpolation is performed without picture element magnification as described above, it is not possible to avoid deterioration of the image quality due to interpolation distortion so as to supplement the enlarged interpolation area with weighted mean values of known data. Conversely to as described above, when the picture element density of an original image is high at "several thousands x several thousands" per screen, the correlation between adjacent picture elements is extremely high and so in principle, it is possible to have compression of the high-quality image information but as has been described, a conventional image information compression system has the disadvantage that the compression ratio cannot be increased since it is a condition for the number of picture elements is in agreement between the original image and the decompressed (restored) image.